The roles of the putative avian oncornavirus-induced tumor antigen (TSSA) as distinct from the virus envelope antigens (VEA) as relevant antigens and their relative importance in the immunological response of avian species to tumor induction have not been well defined. The notion that cellular immunity to TSSA is the dominant determinant in infection with ATV has been accepted mostly in the light of a lack of clear-cut evidence as to the role of other antigens or other immune mechanisms. There is little evidence that such a TSSA exists, much less that it is the sole or main functional determinant of the ultimate outcome of host infection with ATV. We, therefore, propose to define the relevant antigens, viral envelope antigens, tumor-specific surface antigens (VEA, TSSA) or others involved in tumor recognition in chickens and to determine the relative contributions of the cellular and humoral limbs of the chicken immune system in tumor growth and rejection in vivo as assessed by in vitro correlates of immunity. We will also further investigate the immune competence of birds congenitally infected with avian leukosis virus (ALV) to determine if leukocytes (T and B cells) from these birds fail to recognize VEA or TSSA of homologous and heterologous subgroups of ALV and if leukocytes deliberately infected in vitro, as well as in vivo with ALV can recognize TSSA or VEA. In addition, we will attempt to define the importance of humoral immune mechanisms such as antibody dependent cellular cytotoxicity (ADCC) in birds bearing RSV-induced tumors and in birds infected with ALV and attempt to correlate these with other parameters of the immune response as they effect the outcome of ATV-induced neoplasia.